The present invention relates to a bridged driving amplifier for driving a capacitive load which is coupled between a first and a second output terminal of the bridged driving amplifier, which bridged driving amplifier comprises a first driving section coupled between a first supply rail and the first output terminal, a second driving section coupled between the second output terminal and a second supply rail, a third driving section coupled between the first supply rail and the second output terminal, and a fourth driving section coupled between the first output terminal and the second supply rail, whereby the bridged driving amplifier is AC-driven such that the first and the second section, when driven, cause an output voltage across the capacitive load of a given polarity, and the third and the fourth section, when driven, cause an output voltage across the capacitive load of a polarity opposite to the given polarity. Such a bridged driving amplifier can be used in a telecommunication device such as a wired telephone for driving a piezo electrical acoustic transducer for generating a ringing signal, or any other bridged driving amplifier used for driving a capacitive load and driven by an AC-signal. The transducer can be a capacitive transducer having a relatively low dissipation factor and can thus also be a piezo fan, or the like.
The present invention further relates to a telecommunication device comprising such a bridged driving amplifier.
A bridged driving amplifier of the above kind is known from the Data Sheet of the UBA1702 Integrated Circuit, Philips Semiconductors, Jan. 9, 1996, pp. 1-24. On page 4 of this data sheet a block diagram of the UBA1702 is given. Shown is a bridged piezo driving amplifier for driving a piezo electrical acoustic transducer for generating a ringing signal at a typical frequency of 1 kHz. Such a conventional bridged driving amplifier comprises four driving sections of which two are active at a time, for each AC-cycle of an input signal. Driving the bridged driving amplifier causes a switching sequence of charging the capacitive load to a given voltage with a given polarity, discharging the capacitive load, and charging the capacitive load to a voltage of a polarity opposite to the given polarity. This sequence is a cyclic process comprising four states. The conventional bridged driving amplifier is not very efficient because for both charging and discharging currents are drawn from the current supply. Particularly in telephone applications it is desirable to have a more efficient bridged driving amplifier for driving a capacitive ringer.
The German patent DE 35 05 478 describes a more efficient bridged driving amplifier. It is proposed to keep output terminals of the bridged driving amplifier at the same potential during discharging of the capacitive load. No detailed embodiments are shown, only a schematic operation of such a sequence switching. The present invention is aimed to give different solutions to the same basic problem.